Method of visualizing flow patterns



Nov. 3, 1959 R. E. OPDYKE 2,910,865

METHOD OF VISUALIZING FLOW PATTERNS Filed Aug. 30. 1956 United StatesPatent Ofiice 2,910,865 Patented Nov. 3, 1959 METHOD OF VISUALIZING FLOWPATTERNS Richard E. Opdyke, West Allis, Wis., assignor to Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

Application August 30, 1956, Serial No. 607,164

8 Claims. (Cl. 73-147) The present invention relates to a method ofanalysis and more particularly to a method of visualizing the flowpatterns of noncombustible combustion supporting gas streams.

In the selection of conduit for containing a desired flow of gaseousfluids, it is frequently vital that the characteristics of gaseous flowthrough conduit of various geometric configurations be determined topermit the utilization of conduit most properly suited to the desiredflow. The characteristics can best be determined by creating flowthrough a prototype and analyzing its flow pattern provided that patternis true.

A further area in which knowledge of the characteristics of gaseous flowis vital is in the design of articles, such as aircraft, which operatein gas streams under flow conditions assimilated by the stream inducedin the prototype. Again, it is essential that the flow pattern be true.

The problem of creating true gas flow patterns in prototypes of conduitand other aerodynamic apparatus has perplexed men in that art for manyyears. The problem is particularly aggravated in regions of flow havingReynolds numbers in excess of about 3,000 because the flow becometurbulent in character.

. Basically, the prior art techniques or methods of visualizing gas flowfall into three categories, namely: (1) the contamination of the gaseousfluid with foreign matter; (2) the utilization of optical efiects; and(3) especially prepared flow passage boundaries.

The present invention reates to the first of these categories, to wit,the contamination of the gaseous fluid with foreign matter. The priorare methods in this category include the introduction of balsa Wooddust, elongated ribbons and strings, cotton tufts, and smoke trails. Ofthese, the introduction of smoke is perhaps the most successful but evenit is limited to streamline or laminar flow, i.e., flows having aReynolds number of less than 3000 and most generally less than 2100.These methods are further limited in that they are not adaptable to flowthrough rotating machine elements, such as blower impellers.

The smoke method specifica ly comprises introducing smoke into a conduitthrough which a gas flow has been created and observing, through atransparent Wall in the conduit. the path followed by the smoke as it iscarried by the gas. With streamline flow, the smoke provides a decentlaminar flow pattern having discrete paths. With turbulent flow, thesmoke, in response to the turbulence, diffuses into a single cloud andno discrete paths are observable. Consequently with respect to turbulentflow, the smoke technique is virtually useless.

The other foreign particles enumerated above are subiect to the samegeneral limitations as the smoke in varying degrees, i.e., independentpaths cannot be observed. Furthermore, use of all of these foreignparticles to achieve results usually requires costly and complicatedequipment.

In addition to teaching the introduction of the aforementioned foreignmatter into the gaseous fluid flow as a usual means for visualizingsubsonic flow having low Reynolds numbers, the prior art teaches usingespecially prepared boundary patterns as another means for. determiningthe characteristics of subsonic flow and optical effects as the usualmeans for visualizing transonic and supersonic flow. Inasmuch as thepresent invention does not relate to the concept of either especiallyprepared boundaries or optical eflects, these techniques will not befurther discussed.

In all the know prior art, there is no teaching of a method foraccurately representing for visualization and/or otherwise recording theflow pattern of gases in the subsonic range at Reynolds numbers inexcess of about 3000 and through moving or rotating machine elements. Aneed for such a method is very real and ver much present.

The present invention proposes to satisfy that need by a methodcomprising the introduction of low mass selfilluminating tracerparticles into a gas stream for observing and/or otherwise recording thepaths of the particles as they are borne by the stream and by variouscompositions of matter of which the particles are made, each of saidcompositions consisting of carbon, admixed with an oxidizing agent anda'binder. A reducing agent may also be incorporated into the admixturewhen certain flow conditions exist as will be more fully explained.

Accordingly, one of the primary objects of the present invention is toprovide an improved method for visualizing flow patterns of gaseousfluids which is not limited to any particular range of Reynolds numbersand which provides equally satisfactory results regardless of thevelocity of the fluid flow.

Another object of the present invention is to provide a method ofvisualizing flow patterns of gaseous fluids in which the flow pattern isaccurately reflected by selfilluminating tracer particles which areintroduced into and borne by the fluid stream.

Another object of the present invention is to provide an improved methodfor visualizing gas flow patterns in curved conduit by introducing intothe gas flow particles having a sufliciently low mass to be carried bythe fluid stream without being detoured by centrifugal action as wouldbe characteristic of particles of larger mass.

A still further object of the present invention is to provide animproved method for visualizing flow patterns which is easily and simplyperformed and which does not require costly and elaborate setups andequipment.

An even further object of the present invention is the provision of animproved method for visualizing flow patterns utilizing aself-illuminating tracer particle having sufficiently low mass torespond to the velocity component of the fluid flow in the direction offlow to reflect a true pattern of that flow and to resist forces whichmight otherwise distort the pattern of flow.

A still further object of the present invention is the provision of animproved method for visualizing flow patterns by which subsonicturbulent flow through moving or rotating machine elements may be easilyand readily determined.

These and still further objects will become apparent from the followingdetailed description when read in conjunction with the accompanyingdrawing in which:

Fig. 1 is a view in elevation of apparatus by which the presentinvention may be utilized; and

Figs. 2 and 3 are elevations of various sparkler configurations.

In Fig. 1, a'typical'aerodynamic prototype 11 is supported by suitablesupports 12. A transparent plate 13 is disposed in the outer wall of alongitudinal portion 14 of prototype 11 and a transparent plate 15 isdisposed in the outer wall of 'elbow 16. Transparent plates 13, 15

3 may be disposed in the outer wall of ariy portion of the prototype toobserve the flow pattern in that portion since the position of plates13, 15 in Fig. 1 is merely exemplary. Or the entire prototype may bemade of transparient :inat'erial when testconditions dictate that it beso made.

To analyze and observe the flow pattern through the longitudinal portion14 f the protoype 11, a Sparkler 21 is inserted in the prototype as at22 and is supported by any suitable manner, such as by hand 23; Thegaseous stream is created through the prototype in any suitable mannersuch as running a blower 2 4 having its outlet in register withprototype 11. Sparkler 21 is here shown un'ignited.

The method or the present invention specifically com= prises theintroduction into a gaseous stream of burning or glowing particles of'su'fliciently small mass that they are carried by the fluid flow andare not adversely infiu= enced by inertia or centrifugal forces. Byeither visual or photographic analysis of the luminous particle tracesor paths through a wholly or partly transparent prototype, the gas flowpattern may be studied precisely and may be the subject of photographicanalysis.

In addition to the utilization of sparklers in an improved method ofvisualizing gas flow by burning the sparklers and introducing theresulting sparks into a flowing gaseous stream, the present inventionfurther embraces certain compositions of pyrotechnic matter from whichthe sparklers are made.

Certain characteristics are desired for a sparkler comprising acomposition conforming to the present invention They are that theSparkler shall: burn and emit sparks; be self-propagating; not flame;not smoke excessively; not burn too rapidly; not emit ash or otherresidue; and have a physical configuration which is adaptable toprototypes of many geometric configurations. Further, the emittedsparkshall be characterized in that it shall: be self-illuminating; havea mass which is sufliciently low to create a balance between the drag,S'WpDv, (where r 114; #:Viscdsity of the gas; Ddi= ameter of particle;and v,=radial velocity of particle), and the centrifugal force, mvf/f(where m' in'ass of particle; v 'tangential velocity of article; and rradius or curved section), acting on the particle in curved sec= trons,-and between the drag and the forces acting on the particle in straight"sections; have a long life; and have a visible brilliance.

The sparklers utilized may be or any suitable confi oration such as willgive a maximum dispersion of sparks ihto' the fluid stream and arepreferably limited only b the geometry or the prototype to be analyzed.For exam- }fl, in tli afifilyzifiiclfl of fluid flow through the;Cylindrical tubeor Fig. 1, a straight Sparkler 21 (shown enlargedsparkles Z1 iil Fig. 2) gives l-il ifiOSt desirable fes'llltS since itETEWGTQS ih HOW pfbfilt Othi prototypes may be better suited to aspa-rider hoop (shown as 21' in Figs 3)= The sparklers may be preps-redaii'y suitable method such as that by which commercial Fourth of Julysparklers are made, to Wit; the dry it'lgidiflis, add Stifiiifitwater toform it viscous paste, deposit the paste on a wire and dry the coatin onthe wire. The paste can be deposited-on the wire by molding, dipping orothersuitable means. It is ref rred that the wire be shaped beforecoating since the dry coating has a tendarray to chip when bent.

While the methods of preparation are similar, commercial sparklers donot particularly lend themselves to the present invention because themass of the iron particles they use is generally too great to permitburning iron particles to freely follow the gas flow. Comparative testswere conducted utilizing as the source of sparks, first, the so-calledFourth of July or commercial sparkler and, then, the sparklers ofthepresent invention. In both runs, the sparks were introduced into an air4 stream passing through an elbow at 60-80 fps with a Reynolds number ofabout 45,000. It was readily observed that the commercial sparks,because of the inertia resulting from their larger mass, ricochet .offthe inner walls of the elbow instead of following the air stream;whereas the carbon sparks of the present invention, because of theirsmaller mass, follow the air stream.

The importance of the sparks having a low mass is further apparent, bothin the detection of vortices and in the location of leaks in theconduit.

According the present invention further includes various sparkleicompositions which provide all of the characteristics desired for usewith the present method. The particles of these compositions arecharacteriZed by being self-illuminating and having sufiiciently lowmass to be carried by the fiuid stream.

Sparkler compositions which give most satisfactory results when employedin the method of the present invention contain carbon, sugar, deXtriile;potassium chlorate, barium nitrate and aluminum. "Of these ingredients,the carbon is the source of the sparks which are carried by the gasstream. Sugar (C H O and deir'trine (Gail- 6 act as binders and as asource of readily oxidizable carbon. Care should be exercised not to use"more dextrine than sugar because excessive dextrine causes theoccurrence of a liquid has during burning which deters satisfactorcombustion. On the other hand, excessive sugar, 'i.'e., in proportion tothe total ingredients in the nurture, results in inadequate binding andcornbustion residue is introduced into the gas stream. As a secondaryeffect, it is noted that the rate of combustion can bevaried by alteringthe sugar-to-dextrine ratio since sugar increases the rate of Combustionand dextrine reduces it. v

I Both potassium chlorate (KClO and barium nitrate (Ba(NU act asoxidantsand supply oxygen to support combustion. It is no ed that the rate ofcombustion may also be controlled by varying the potassium-tobariumratio in the mixture since potassium chlorate increases the burning rateand barium nitrate reduces it. Aluminum is used to increase thetemperature of combustion and, though only 'optional in sparklers to beused to visualize streams "of low velocity, is a highly desirableingredient: forsparklers which will be used to visualiie streams of highvelocity. The passage of high velocity flow over a Sparkler whichcontains no aluminum transfers heat from the burning Spa kler so rapidlythat soon the s'parkler is unable to kindle the unburned portion or thes 'arlder as it attempts to self-propagate. Consequeiitliy, when flowconditions are to be analyzed which will eifect a rapid heat transfer,the aluminum offsets the effector the rapid flow by providing additionalheat. Thus even though the heat transfer continues, there is suhicientresidual heat at the s arkler to keep the burning particles ld dling theunburned particles to effect the desired self-propagation. v

Thus, the compositions used in the practice of the present invention maybe altered by the skilled artisan to lit the particular How conditionsdesired for study. If an increased burning rate is desired, the suandextrine ratio may be increased to a point where dextrine iseliminated completely so long as the ratio of sugar to the total comosition reinains substantially in the range disclosed by the examplesset forth below. And the burning rate may likewise be increased byincreasing the potassiumzbarium ratio to a point where barium iseliminated. Conversely, the burningrate may be retarded by reducing thesugarzdextri-ne and potassiumzbarium ratios although it is preferablethat the suga-rzdextrine ratio be not less than 1:1.

Further, if high heat is desired, aluminum may be included; In all ofthe compositions, however, it is essential that they include a binder,such as sugar, an oxidant, such potassium chlorate, and a quantity ofture to form a thick paste, coating a wire form with the thick paste,and drying the coated wire for approximately twenty-four'hours at roomtemperature.

Example 1 The following ingredients comprise Mix No. 1:

Grams KClO 6.5 83(N03): 7.5 Aluminum 0.84 C H O 2.33 CHI-133011 Carbon2.46

Example 2 The following ingredients comprise Mix No. 2:

Grams KClO 0.5 Ba(NO Aluminum 1.0 12 22 11 Carbon 1.0

Example 3 The following ingredients comprise Mix No. 3:

Grams KClO 1.0 Ba(NO 1.0 Aluminum 1.0 C H O 0.5 C H O 0.5 Carbon 1.0

Example 4 The following ingredients comprise Mix No. 4:

Grams KClO 1.0 CmHnOn 1.0 Carbon 1.0

The carbon of all four mixes may be either finely powdered wood charcoalor graphite, and preferably less than forty microns in diameter. Bonecharcoal is not satisfactory because of its low carbon and highphosphate content.

Although the sparkler may be of any desired shape or form so long as itdoes not disturb the flow pattern (see Figs. 2 and 3), a one-fourth inchdiameter sparkler has been found satisfactory in practicing the methodwith respect to most conventional prototypes having diameters of two andone-half inches or larger.

When the sparkler has been prepared and after the gas stream isinitiated through the desired prototype, the sparkler is strategicallyplaced in the stream and ignited. The sparks which are emitted from thesparkler then provide a brilliantly accurate and dramatic trace patternof the flow through the prototype and may be readily photographed, ifdesired, to provide a permanent record. Incidentally, excellent resultsare obtained using both motion picture and still picture cameras, and,if an immediate picture is needed, the Polaroid Land Camera(manufactured by the Polaroid Corporation, Cambridge, Massachusetts)provides pleasing results. Several photographic records have been madeof the particle paths in ranges of turbulent flow and all provideddiscrete particle paths such as have not been obtainable heretofore. Itis to be noted that, in the flow patterns analyzed by the practice ofthe present invention, there is'no diffused blending of the particlesinto a single cloud mass as was characteristic of the smoke technique.

The terms gas, gaseous fluid and fluid are used interchangeably hereinto define a gas, such as air, which will support combustion but which isnot itself combustible.

It is understood that the foregoing description of one embodiment of themethod and several exemplary sparkler compositions is for illustrativepurposes only and that the present invention is not intended to belimited thereto. Rather, it is intended that such obvious modificationsand equivalents as may readily occur to one skilled in the art fromknowledge of this disclosure are likewise embraced by the presentinvention which is to be limited only by the scope of the appendedclaims.

What is claimed is:

1. The improvement in the art of visualizing the flow patterns of astream of combustion supporting noncombustible gas passing through anaerodynamic prototype comprising introducing a burning tracer particleinto the stream, and releasing said particle into the stream to becarried by the stream, said particle having sufficiently low mass tofollow the velocity component of the stream in the direction of flow andto accurately reflect by its physical movement the pattern assumed bythe flow.

2. The improvement in the art of visualizing the flow pattern of astream of combustion supporting noncombustible gas passing through anaerodynamic prototype comprising introducing discrete incandescenttracer particles to the stream, and releasing said particles into thestream to be carried by the stream, said particles being characterizedby a mass sufficiently low and a size sufiiciently small to enable it toresist the influence of forces acting thereupon to deter it fromreflecting the true flow pattern of the stream.

3. A method of visualizing the flow pattern of a gas combustionsupporting noncombustible gas stream passing through an aerodynamicprototype comprising presenting to the gas stream a sparkler comprisinga sparking composition of pyrotechnic matter; burning said sparkler tocreate sparks; and causing said sparks to be emitted from the sparklerinto the stream to be carried by the stream.

4. The method of visualizing gas flow patterns in conduit comprisinginitiating gas flow through a conduit; introducing self-illuminatingpyrotechnic tracer particles into said flow, and releasing saidparticles into the stream to be carried by the stream, each of saidparticles having sufficiently low mass to effect a balance between thedrag of the particle and the inertia and centrifugal forces acting onthe particle, to enable the particles to follow the velocity componentof the gas flow in the direction of the flow thereby accuratelyreflecting by their physical movement the pattern assumed by said flow.

5. The method of visualizing gas flow patterns in conduit comprising:initiating gas flow through a conduit; introducing discrete incandescenttracer particles into said flow, and releasing said particles into thestream to be carried by the stream, said particles being characterizedby a mass sufliciently low to resist the influence of inertia andcentrifugal forces acting thereupon; and recording the paths of saidparticles in said flow.

6. The method of visualizing the flow pattern of an air stream passingthrough an aerodynamic prototype comprising creating an air streamthrough an aerodynamic prototype; and causing burning sparks consistingessentially of carbon to be introduced into and carried by the airstream to accurately reflect the flow pattern of the air stream.

7. The method of visualizing the flow pattern of an air stream passingthrough an aerodynamic prototype comprising creating an air streamthrough an aerodynamic prototype; and causing burning sparks consistingessentially of carbon to be introduced into and carried by the 7 airstream, said carbon sparks being characterized by a critical diameter ofnot more than '40 microns.

8. The improvement in the art of visualizing the flow pattern of astream of combustion supporting noncombustible gas passing through anaerodynamic prototype comprising: preparing a sparkler comprising carbonparticles having a diameter of 40'microns or less; initiating a streamof combustion supporting noncombustible gas through an aerodynamicprototype; presenting said sp'arkler to said stream; burning saidsparkler to liberate said carbon particles in a burning state; andutilizing said stream to prolong the bur-nin'gof said particles which '00 have entered into and are carried by said stream and cause 'visiblerecognition of the flow patternof said stream.

References Cited in the file of this patent UNITED STATES PATENTS1,676,984 Fales et a1. July 10, 1928 2,131,041 Hale Sept. 27, 19382,616,291 Benedum 'Nov. 4, 1952 2,628,897 Vinton ..Q Feb. 17, 1.953.2,637,208 Mellen May 5, 1953 2.795.738 Holliday -r----r---.---- June 11,19,57

1. THE IMPRIVEMENT IN THE ART OF VISULATING THE FLOW PATTERNS OF ASTREAM OF COMBUSTION SUPPORTING NONCOMBUSTIBLE GAS PASSING THROUGH ANAERODYNAMIC PROTOTYPE COMPRISING INTRODUCING A BURNING TRACER PARTICLEINTO THE STREAM, AND RELEASING SAID PARTICULES INTO THE STREAM TO BECARRIED BY THE STREAM, SAID PARTICULE HAVING SUFFICENTLY LOW